1. Field of the Invention
This invention relates to an optical module used for an optical interconnection.
2. Description of the Related Art
In recent years, optical interconnection, which is a technology for transmitting a signal at high speed in a system apparatus or between system apparatuses, has grown. That is, the optical interconnection is a technology to treat an optical component as if it is an electrical component, and to surface-mount the optical component on a mother board or a circuit substrate of a PC, a vehicle, or an optical transceiver.
As a conventional optical transceiver used for the optical interconnection, an optical module 191 is shown in FIG. 19 (e.g., referring to JP-A-2005-292739).
The optical module 191 includes a substrate 192 having a cavity which is open at an upper part of the substrate 192, a transparent plate 194, including a glass or a sapphire glass, having a circuit pattern 193 on one surface of the transparent plate 194, and an optical element 195 (photoelectric conversion element) mounted on the circuit pattern 193. The optical module 191 is hermetically sealed by connecting the substrate 192 with the transparent plate 194. Further, a fiber block 196 is mounted on the optical module 191.
However, in the conventional optical module 191, it is difficult to form the circuit pattern 193 on the transparent plate 194.
Further, when the circuit pattern 193 is formed on the transparent plate 194 made of glass or sapphire glass, since it is difficult to form a through-hole in the transparent plate 194, the circuit pattern 193 cannot be formed on both sides of the transparent plate 194, and thus, the transparent plate 194 having the circuit pattern 193 only on one side thereof can be used.
Consequently, a circuit area of the transparent plate 194 becomes large, and thus, the entire optical module 191 becomes large.
A reason that it is difficult to form the through-hole in the transparent plate 194 is that a material such as glass or sapphire glass is hard, and it is difficult to form a fine hole. Further, even if the fine hole is formed, a crack may occur in the transparent plate 194.
Further, even if the fine hole is formed, it is necessary to fill an inside of the through-hole by a metal plating such as Cu or Au in order to place the optical element 195 on the substrate 192 and to hermetically seal the optical element 195. However, since a linear expansion coefficient of the glass or the sapphire glass is much less than that of the metal, a detachment of the metal occurs by a temperature cycle, and the hermetic seal is broken.